1. Field of the Invention
The invention generally relates to an electromagnetic wave absorber and, more particularly, to an electrically conductive surface element incorporated in a non-combustible absorber of electromagnetic radiation and to a process for producing an electrically conductive surface element of this type.
2. Background Discussion
In the case of existing flight safety systems, very short-wave electromagnetic waves, in particular radar waves, are used to locate and identify aircraft. This is true of both civilian and military air traffic. Flight safety systems of this type are impaired by the reflection of radar waves, particularly, for example, from external facades of buildings in the vicinity of airports, because the reflection of these radar waves can lead to considerable interference in the ability of such flight safety systems, using radar, to locate aircraft.
Although provision can be made, on the ground, for filtering out the effects of unwanted reflected radar waves using specific technical devices, this is hardly practicable on an aircraft due to the lack of space and weight restrictions. For this reason, it is very important that the reflection of electromagnetic waves, in particular radar waves, at external facades of buildings in the vicinity of airports, be eliminated to a large extent.
In order to solve this problem, it has already been suggested that radar absorbers, in the form of a surface element which absorbs radar waves, should be used in the construction of the external facade of buildings in the vicinity of airports. Such surface elements typically comprise panel sections or layers, made from mineral wool, and panel sections or layers, made from an electrically conductive material, these different layers of material being arranged in an alternating fashion in the manner of a lamellar structure. The lamellar structure is placed into a cassette-type frame and secured to the building by the frame to form the radar absorber.
However, in practice, such radar absorbers cause considerable difficulties since adherence to critical or optimum values for absorption is important for an absorber of this type to achieve a sufficient level of reflection or absorption with regard to the radar waves. Thus, in the case of radar absorbers of the multi-layer lamellar structure described above, the reflection or absorption level does not only depend on the relative distances between the panels of mineral wool and the electrically conductive layers, which distances are adapted to the particular type of radar waves to be absorbed, but also on the amount and distribution of an electromagnetically active material, embedded in the intermediate layers between the mineral wool panels, which is responsible for providing the conductivity of these electrically conductive intermediate layers.
Obtaining a good absorption level depends mainly on adherence to very narrow application tolerances during the embedding of the electromagnetically active conductive material in the intermediate layers between the mineral wool layers. However, these application tolerances are difficult to produce to industrial standard sizes using materials of this type.
Furthermore, both the embedding of the electromagnetically active conductive material, which is mainly responsible for the radar-absorbing properties of the layered structure, and the use of binders for the layered structure, lead to the multi-layer systems of this type being combustible. As a consequence, such absorbers can no longer be included in construction materials class A according to DIN 4102.